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What is Real-Time?What is Real-Time?Posted Dec 29, 2004 8:30 UTC (Wed) by chel (guest, #11544)In reply to: What is Real-Time? by jd Parent article: Where Is Real-Time Linux? (TechNewsWorld)
Your two examples show the misconception.
In your first example, sampling audio for recording, the real-time constraints are not an OS constraint. Sampling and buffering is done in hardware, so the only thing left is a speed constraint. In a computer system you will find a lot of these real-time constraints solved in hardware.
In your second example, the flight simulator, there are real "real-time" OS constraints. You have to create a fluent simulation, based on input. This simulation should be available here and now. The actions on input should result with a small end fixed delay in corresponding output. Fuzzyness in the delay is not acceptable.
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What is Real-Time? Posted Dec 30, 2004 8:13 UTC (Thu) by Wol (guest, #4433) [Link] This sounds back to front to me. Yep, when sampling audio, you just have a hardware latch. But it IS a realtime response, because if the computer doesn't get round to reading the latch in time, you have lost data. In other words, there is a deadline, and a missed deadline causes ?irrecoverable? problems.
Your second example, the simulator, is NOT realtime. What do you mean by "here and now"? Mechanical systems don't respond immediately, and on a real aircraft, say, there is a time lag between pushing the stick and the ailerons responding. And then there's a further delay until the aircraft's attitude responds. So who cares how quickly a flight sim responds, so long as it's pretty close to what would happen in real life.
Actually, there was an example on Risks, where an airline had set the simulators to respond over-aggressively, and a disaster was blamed on this. The simulator taught pilots to respond aggressively to control problems, and then when a pilot did this in real life, the resulting stresses ripped the airliner's tail off :-(
Cheers,
What is Real-Time? Posted Dec 30, 2004 20:10 UTC (Thu) by chel (guest, #11544) [Link] What do you mean by "here and now"?
The actions on input should result with a small and fixed delay in corresponding output. Fuzzyness in the delay is not acceptable.
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